This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A064070 #18 Feb 16 2025 08:32:45
%S A064070 2,126,49410,48649086,89434106370,264235243691646,1145011717430672130,
%T A064070 6841110155700330881406,53899295662946509072626690,
%U A064070 541439307193573593050370186366,6754273504043546592593642328610050,102439130403410639137159601119206854526
%N A064070 Generalized Euler number c(9,n).
%H A064070 Matthew House, <a href="/A064070/b064070.txt">Table of n, a(n) for n = 0..174</a>
%H A064070 D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1967-0223295-5">Generalized Euler and class numbers</a>. Math. Comp. 21 (1967) 689-694.
%H A064070 D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1968-0227093-9">Corrigenda to: "Generalized Euler and class numbers"</a>, Math. Comp. 22 (1968), 699.
%H A064070 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EulerNumber.html">Euler Number</a>.
%F A064070 a(n) = (2*n)!*[x^(2*n)](sec(9*x)*2*cos(3*x)^2). - _Peter Luschny_, Nov 21 2021
%p A064070 egf := sec(9*x)*2*cos(3*x)^2: ser := series(egf, x, 24):
%p A064070 seq((2*n)!*coeff(ser, x, 2*n), n = 0..10); # _Peter Luschny_, Nov 21 2021
%t A064070 Range[0, 22, 2]! CoefficientList[Series[2 Sec[9 x] Cos[3 x]^2, {x, 0, 22}], x^2] (* _Matthew House_, Oct 27 2024 *)
%Y A064070 Row 9 of A235605.
%Y A064070 Cf. A064074, A349268, A349264.
%K A064070 nonn,easy
%O A064070 0,1
%A A064070 _Eric W. Weisstein_, Aug 31 2001